1. Field of the Invention
The present invention relates to a digital image forming apparatus, for use in a digital copying machine, a digital facsimile, etc. The invention relates, particularly, to an digital image forming apparatus having simple structure and operation for detecting a center portion of a book document.
2. Discussion of Background
In Japanese Patent Laid-open Publication No. 63-41148, an image forming apparatus is described, in which a photo sensor is installed on a document board to detect a center position of a book document. Moreover, in Japanese Patent Laid-Open Publication No. 59-170856, an apparatus, in which a detector for detecting the document size on a platen glass board and a discharger for discharging and erasing a part of a photoconductive element are installed, is described. Then in the apparatus, an unnecessary part of a photoconductive element is prevented from developing by driving a discharger on the basis of a signal of a document size.
In one image forming apparatus, the photo sensor is installed on the document board to detect the center portion of the book document. Moreover, in the other apparatus for preventing a part of a photoconductive element from developing, as the discharged and erased part on the photoconductive element is decided only by the document size, a necessary part of the document may be erased when the document is shifted from the correct position on the platen glass board.